The present invention relates to a circuit for amplifying and shaping an AC signal obtained from a tap of voltage divider including at least one magneto-resistor.
A circuit with a bridge circuit consisting of four magneto-resistors is described in "Elektronik", No. 10, May 17th, 1985, pp. 99 to 101, where on p. 100 an operational amplifier is used as a signal amplifier, and a Schmitt-trigger-connected operational amplifier as a pulse shaper. The supply voltage is assumed to be constant, and temperature compensation is effected by a PTC resistor via an additional amplifier and a voltage divider. Each of the leads to the signal amplifier contains a resistor for eliminating any temperature dependence of the gain. The prior art circuit requires at least four connecting leads, namely two for the supply voltage and two for the output signal.
An object of the present invention is to achieve amplification and signal shaping with a minimum of components and connecting leads.
This object is attained by obtaining from the tap of a voltage divider including at least one magneto-resistor a measurement signal having an AC component, and controlling a controllable impedance by this measurement signal. Since the circuit requires only a small number of small components, the latter can be housed in a single, two-lead package. Further advantageous details and will now be described with the aid of the embodiments illustrated in the accompanying drawings, in which: